Determined to put on a show of "solidarity" for Boston, London Marathon organizers are refusing to cave in to the threat of terrorism and will stage their race on Sunday.

The British capital has long been a top target for terrorists and these concerns have only intensified ahead of this weekend's race after Monday's harrowing scenes at the Boston Marathon, where bombs killed three people and injured many more.

However, British sports minister Hugh Robertson said the London Marathon, watched by an estimated 500,000 spectators and run through some of the city's most recognizable landmarks, should be staged as planned to show "we won't be cowered by this sort of behaviour."

"The best way for us to react is to push ahead with the marathon on Sunday, to get people on the streets and to celebrate it as we always do in London," Robertson told the BBC on Tuesday.

"These are balance of judgments, but we are absolutely confident here that we can keep the event safe and secure. I think this is one of those incidents where the best way to show solidarity with Boston is to continue and send a very clear message to those responsible."

Security is being scrutinized after the events in Boston, where two bombs exploded near the finish of the marathon.

Prince Harry, the patron of the London Marathon Charitable Trust, will attend Sunday's race and make the presentations to the winners.

"The London Marathon fully expects at this stage … [to] go ahead as planned on Sunday although we are continuing to review security with the Metropolitan Police in the coming days," Nick Bitel, chief executive of the London Marathon, said on Tuesday in an interview on the race website.

"The London Marathon will be in touch with the runners through their email and they will hear from us on a daily basis in that way. We will try to keep updating our runners throughout this period."

Bitel told the BBC: "When you have an event of any nature — a marathon, parade — it's only as safe as the city itself. If it's not held in a stadium, you can't do a lockdown like you may do in a building."

Mo Farah, Britain's double Olympic long-distance champion, will be running a half-marathon, while the three medallists from the men's marathon at the 2012 London Games are also among the 37,500 entries.

'Beautiful running festival'

Sunday's race is one of six in the World Marathon Majors series along with Tokyo, Boston, Berlin, Chicago and New York.

Belgrade is among other cities staging marathons this weekend, with organizer Dejan Nikolic expressing confidence that the race will be safe and a "beautiful running festival."

"We will do our best so that this year the security level is even higher," Nikolic said.

In 2005, suicide attacks on the public transport system in the British capital killed 52 people. London and mainland Britain also face a moderate threat from Northern Ireland-related terrorism, according to the government, and a massive security operation was put in place last summer to protect the successful London Olympics.

This year's Boat Race between English universities Oxford and Cambridge went ahead amid tightened security after a protester jumped into the River Thames last year and narrowly avoided being hit by the oars of the two crews. Royal Marines were stationed along the length of the nearly seven-kilometre course.

Police already were preparing a major security operation in London for Wednesday's ceremonial funeral for former Prime Minister Margaret Thatcher, an event at St. Paul's Cathedral that will be attended by Queen Elizabeth II and dignitaries. The plans call for a procession through the streets of London, with Thatcher's flag-draped coffin to be carried on a horse-drawn carriage.

The funeral's security plans are expected to be reviewed in light of the bombings at the Boston Marathon, which is held each year on Patriot's Day.

"It's particularly ghastly that this should have happened on a day of great national celebration in Boston — on a day when so many families were out on the streets and when so many people were raising millions of dollars for charity," Robertson said. "That makes it worse.

"It's utterly horrifying and completely appalling. It's difficult to think of a more ghastly event that this should be perpetrated upon."